This invention relates in general to balance weights for balancing an unbalanced rotatable member for rotation. More specifically, this invention relates to an improved structure for a balance weight adapted to be adhered to a driveshaft tube connected between an engine/transmission assembly to an axle assembly in a vehicular drive train assembly for rotatably balancing the driveshaft tube during use.
Torque transmitting shafts are widely used for transferring rotational power between a source of rotational power and a rotatably driven mechanism. An example of a torque transmitting shaft is a driveshaft tube used in a vehicle driveshaft assembly. The driveshaft assembly transmits rotational power from a source, such as an engine, to a driven component, such as a pair of wheels. A typical vehicle driveshaft assembly includes a hollow cylindrical driveshaft tube having an end fitting secured to each end. Usually, the end fittings are tube yokes that are adapted to cooperate with respective universal joints. For example, a driveshaft assembly of this general type is often used to provide a rotatable driving connection between the output shaft of a vehicle transmission and an input shaft of an axle assembly for rotatably driving the vehicle wheels.
Ideally, each driveshaft tube would be manufactured in the shape of a cylinder that is absolutely round, absolutely straight, and has an absolutely uniform wall thickness. Such a perfectly shaped driveshaft tube would be precisely balanced for rotation and, therefore, would not generate any undesirable noise or vibration during use. In actual practice, however, the driveshaft tubes usually contain variations in roundness, straightness, and wall thickness that result in minor unbalances when rotated at high speeds. To prevent such unbalances from generating undesirable noise or vibration, therefore, it is commonplace to counteract such imbalances by securing balance weights to selected portions of the driveshaft tube. The balance weights are sized and positioned to counterbalance the unbalances of the driveshaft tube such that it is balanced for rotation during use.
Traditionally, vehicular driveshaft tubes have been formed from steel alloys or other metallic materials having relatively high melting temperatures. In such driveshaft tubes, welding has been commonly used to secure the balance weights thereto. More recently, however, driveshaft tubes have been formed from aluminum alloys and other metallic materials that are not well suited for welding balance weights thereto, particularly in the high volume quantities usually associated with the vehicular manufacturing industry. Also, driveshaft tubes have recently been formed from composites and other materials that are not suited at all for welding.
To balance driveshaft tubes formed from these alternative materials, it has been proposed to use adhesives to secure the balance weights to the driveshaft tubes. In the past, the balance weights have typically been formed from steel alloy materials. Such steel alloy materials have been found not to interact adversely with the aluminum alloy used to form the driveshaft. Also, steel alloy materials have been found not to be prone to surface oxidation, which can cause undesirable de-bonding of the balance weight from the driveshaft tube. Unfortunately, however, it has been found that balance weights formed from such steel alloy materials were relatively inflexible in comparison with the relatively thin walled aluminum driveshaft tubes to which they were attached. Because of this, it has been found that under certain operating conditions, the aluminum driveshaft tube could flex beyond the ability of the steel alloy balance weight to bend accordingly. When this occurs, the adhesive extending between the outer surface of the driveshaft tube and the inner surface of the balance weight can fracture or otherwise fail, causing the balance weight to fall off of the driveshaft tube.
One possible solution to this problem would be to form the balance weight from a material that is more flexible that steel alloy materials, such as lead. The use of such relatively flexible materials would allow the balance weight to flex with the aluminum driveshaft tube during use, thereby preventing damage to the adhesive extending therebetween. However, it has been found that lead and other relatively flexible materials are prone to surface oxidation, particularly in the presence of some of the materials that are used as adhesives to secure the balance weight to the outer surface of the driveshaft tube. Such surface oxidation can reduce the bonding strength of the adhesive, causing the balance weight to fall off of the driveshaft tube when it is rotated at high speeds during use. Thus, it would be desirable to provide an improved structure for a balance weight adapted to be adhered to an outer surface of a driveshaft tube that can accommodate flexing movement of a driveshaft tube, yet is not subject to surface oxidation or other conditions that might reduce the bonding strength of the adhesive.
This invention relates to an improved structure for a balance weight that is adapted to be adhered to a driveshaft tube connected between an engine/transmission assembly to an axle assembly in a vehicular drive train assembly for rotatably balancing the driveshaft tube during use. The driveshaft tube is preferably formed from an aluminum alloy material and has a balance weight secured to the outer surface thereof to counterbalance the unbalances of the driveshaft tube. The balance weight includes a first inner layer of material and a second outer layer of material that are secured together to form an integral unit. The first and second layers of material may be secured together in any desired manner, such as by adhesives, pressure bonding, tinning, electroplating, and the like. The inner layer is preferably sufficiently flexible to bend with the driveshaft tube during use and is preferably formed from a material that does not react with either the material used to form the driveshaft tube, the material used to adhere the inner layer to the driveshaft tube, or the environment in which the inner layer is used in such a manner as to reduce the ability of the balance weight to be retained on the driveshaft tube. In a first embodiment, the inner layer can be formed from a stainless steel alloy having a relatively small thickness that allows it to bend with the driveshaft tube during use. The outer layer is preferably formed from a material that also is capable of bending with the driveshaft tube during use, but has high weight density so as to be capable of balancing the driveshaft tube while maintaining a relatively small physical size. The outer layer may be formed from lead or a lead alloy material having a relatively large thickness. One or more grooves may be formed in the outer surface of the outer layer to facilitate flexing of the outer layer with the driveshaft tube. The balance weight is secured to the outer surface of the driveshaft tube by a layer of adhesive that bonds the inner layer of the balance weight to the outer surface of the driveshaft tube. In a second embodiment, the inner layer is a relatively thin layer of tin that is electroplated to the outer layer of lead. The balance weight is secured to the outer surface of the driveshaft tube by a layer of adhesive that bonds the electroplated tin layer of the balance weight to the outer surface of the driveshaft tube.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.